Ad hoc networks are the focus of considerable research and development. A key characteristic of these networks is that they do not rely on fixed infrastructure to the extent that other networks such as satellite, cellular, and Wireless Local Area Networks (WLAN) do. Nodes beyond the communication reach of a transmitting node may be reached through intervening nodes providing a relay function. This feature is clearly attractive for tactical (military and police) and first responder (police and fire) applications. This feature is also seen as a method of increasing the coverage of more traditional infrastructure-based networks. When we refer to ad hoc networks in the description of this invention we also refer to ad hoc components of larger communication networks.
Significant standardization efforts are in progress in the area of Mobile Ad Hoc Networks (MANETs) for IP traffic. A MANET is a wireless ad hoc network formed in an arbitrary network topology. Nodes within this network may move arbitrarily causing the network topology to change rapidly. The network does not, in general, depend on any particular node and dynamically adjusts as some nodes join or others leave the network. Although the MANET element of a network is not dependent on fixed infrastructure, elements such as access points (providing access to the Internet) are a key component of many systems that employ MANET protocols.
MANET networks allow quick deployment and adjust as nodes join and leave the network and thus are an obvious candidate for tactical and first responder networks. MANETs are also employed to extend the coverage of more traditional networks, such as WLANs.
Nodes within a MANET are often powered by batteries. Battery run time, regulatory considerations, and detectability considerations limit a node's radiated power. The intended communication range between two nodes often exceeds the radio transmission range, and a transmission has to be relayed by other nodes to reach its destination(s). Consequently, the network has a multi-hop topology, and this topology changes as the nodes move.
The MANET working group of the Internet Engineering Task Force has been actively evaluating and standardizing routing protocols. Because the network topology changes arbitrarily as the nodes move, it is important for a protocol to be adaptive. The Ad Hoc on Demand Distance Vector (AODV) protocol is representative of on-demand routing protocols presented at the MANET working group.
Performance of protocols developed within the MANET working group is severely impacted by the decision to limit “MANET modifications” to elements at the network layer and above. As a result of the Carrier Sense Multiple Access (CSMA) protocols assumed at the Media Access Control (MAC) and Physical (PHY) layers, nodes with a message to relay need to take turns with other nearby nodes attempting to relay the same information. This factor results in dramatic loss of network capacity while increasing transmission latency.
Capacity, latency, and robustness issues of ad hoc networking protocols are key considerations for all ad hoc networks, regardless of whether nodes are mobile or not, and independently of the type of network traffic (IP, Voice, Video, Streaming, etc.). An additional key consideration for mobile ad hoc networks is how the networking protocol accommodates network topology dynamics.